Solar generators usually include electrically connected photoelectric cells each covered by a protective window (or screen or filter). These protective windows (or screens) are intended to protect the photoelectric cells from some kinds of radiation, for example streams of protons and/or electrons, in order to guarantee them a certain service life. Moreover, these protective windows (or screens) having to allow photons to pass through them, they are generally made from a glass material (for example of the “coverglass” type) and glued by means of a transparent glue or adhesive that is not electrically conductive. As these materials are not electrically conductive, they tend to acquire an electrostatic charge, which sometimes causes localized electrical arcing known as primary electrical arcing (or electrostatic discharge (ESD)) between its protective window and the photoelectric cell that it covers or an adjacent photoelectric cell.
Here the expression “protective window” refers to the assembly including the material for protecting the cell (for example the coverglass) and its glue or its adhesive.
As the person skilled in the art knows, a primary electrical arc is in two parts.
The first part is known as the “blow-off”. It takes the form of a current induced by the rapid discharging of the general capacitance of the equipment (for example a satellite) on which the solar generator is installed.
The second part is known as “flash-over”. It takes the form of a current induced by the slow discharging of the protective windows of at least some of the photoelectric cells, by a progressive propagation mechanism at a speed of the order of 104 m/s. This propagation mechanism travels from the protective windows of the cells that are mounted in series to constitute a branch to the protective window of the cell that is the site of the primary electrical arc, because of the plasma that is created between the protective windows of adjacent cells. It also travels from the protective windows of the cells that are part of branches adjacent to the branch containing the cell that is the site of the primary electrical arc to the protective window of the latter cell, because of the plasma and of the circulation of the slow discharge current from the branch that is the site of the primary electrical arc to the adjacent branches, via their electrical connections. The slow discharge current generally circulates via the ends of the branches that are of negative polarity, given that their opposite ends, of positive polarity, are generally provided with current blocking means such as diodes.
This flash-over (or slow discharge) can damage some of the photoelectric cells if its duration exceeds a threshold that depends on the material from which they are produced. This is the case in particular when the photoelectric cells are produced in a semiconductor material such as gallium arsenide (AsGa) and the duration of the flash-over (or slow discharge) is more than approximately 100 μs. This damage reduces the service life of the photoelectric cells (and thus reduces their reliability), which is particularly problematical if they cannot be replaced.